Optical Turnaround System

ABSTRACT

A technique is provided for utilizing an optical fiber in a variety of sensing applications and environments by beneficially routing the optical fiber. A continuous optical fiber is created to provide optical continuity between two ends of the optical fiber. The optical continuity is created with the assistance of an optical turnaround constructed in a simple, dependable form able to control the bend of the optical fiber as it extends through the optical turnaround.

RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.11/779,376, filed Jul. 18, 2007, and entitled “OPTICAL TURNAROUNDSYSTEM.”

BACKGROUND

Optical fibers are used in a variety of sensing and other applications.For example, optical fiber has been used as a distributed temperaturesensor in oilfield applications where the temperature profile can beapplied in, for example, detection of water breakthrough, detection ofleaks, and gas lift monitoring and optimization. The optical fiber isutilized by injecting light into the fiber, measuring the backscatteredlight, and then processing the results to determine temperature alongthe length of the fiber.

Research has shown that distributed temperature sensor measurements aremore accurate when performed in a double-ended configuration such thatoptical continuity exists between two optical fiber ends connected to adistributed temperature sensor control system. By preparing thisdouble-ended configuration, light can be sent through the completelength of optical fiber from both directions and measurement correctionis facilitated. However, the double-ended configuration requires that acontinuous optical fiber extend down into a wellbore for the desiredinterval to be sensed, turnaround, and return to the surface.

Attempts have been made to create turnarounds that route the opticalfiber back to the surface. In one example, the turnaround has beenformed with a metal tube doubled back on itself with both ends connectedto additional tubing. The optical fiber is then routed through thetubing. This technique, however, requires many tubing connections thatreduce system reliability while increasing deployment time. Manyapplications also are subject to space constraints which can createproblems in properly controlling the bend of the optical fiber whenrouted through a turnaround. Exceeding the minimum bend radius of anoptical fiber increases optical attenuation and can ultimately result infiber breakage.

SUMMARY

In general, the present invention provides a system and method forrouting an optical fiber that can be used in a variety of sensingapplications and environments. A continuous optical fiber is createdsuch that optical continuity exists between two ends of the opticalfiber. The optical continuity is created with the assistance of anoptical turnaround constructed in a simple, dependable form able tocontrol the bend of the optical fiber as it extends through the opticalturnaround.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments of the invention will hereafter be described withreference to the accompanying drawings, wherein like reference numeralsdenote like elements, and:

FIG. 1 is a front elevation view of a fiber optic system positioned in awellbore with a corresponding well system, according to an embodiment ofthe present invention;

FIG. 2 is a view of an optical fiber loop that may be adjusted in sizewithin a protective housing, according to an embodiment of the presentinvention;

FIG. 3 is a view of the optical fiber loop illustrated in FIG. 2combined with a seal assembly positioned to seal the protective housingto an optical fiber cable, according to an embodiment of the presentinvention;

FIG. 4 is a cross-sectional view of an optical fiber turnaround,according to an alternate embodiment of the present invention;

FIG. 5 is a cross-sectional view of the optical fiber turnaroundillustrated in FIG. 4 but rotated ninety degrees, according to anembodiment of the present invention;

FIG. 6 is a cross-sectional view of the optical fiber turnaround takengenerally a long line 6-6 in FIG. 4, according to an embodiment of thepresent invention;

FIG. 7 is a front view of an embodiment of an insert that may be used inthe turnaround illustrated in FIG. 4, according to an embodiment of thepresent invention;

FIG. 8 is a top view of the insert illustrated in FIG. 7, according toan embodiment of the present invention;

FIG. 9 is a front view of another embodiment of an insert that may beused in the turnaround illustrated in FIG. 4, according to an alternateembodiment of the present invention; and

FIG. 10 is a top view of the insert illustrated in FIG. 9, according toan alternate embodiment of the present invention.

DETAILED DESCRIPTION

In the following description, numerous details are set forth to providean understanding of the present invention. However, it will beunderstood by those of ordinary skill in the art that the presentinvention may be practiced without these details and that numerousvariations or modifications from the described embodiments may bepossible.

The present invention generally relates to a fiber optic system thatutilizes an optical fiber in parameter sensing applications. The systemutilizes optical fiber arranged in a double-ended configuration toprovide optical continuity between two fiber ends that are connected toan appropriate control unit. The configuration facilitates sensing ofthe desired parameter by, for example, allowing light to be sent throughthe complete length of the optical fiber from both directions. Thearrangement also facilitates measurement correction to provide for moreaccurate measurement of the desired parameter. In one embodiment, thefiber optic system is utilized in a well environment and the opticalfiber is deployed in a wellbore drilled into a geological formationholding desired production fluids, such as hydrocarbon based fluids.

Referring generally to FIG. 1, a fiber optic system 20 is illustratedaccording to one embodiment of the present invention. Fiber optic system20 comprises an optical fiber sensor 22 that may comprise a distributedsensor 24 coupled to an appropriate control unit 26. The control unit 26may be selected from a variety of available optical control systems usedto inject light along optical fiber. The control unit 26 is then used tomeasure the backscattered light and to process the results to determinethe sensed parameter, e.g. temperature, along the length of the opticalfiber. Temperature profiles can be used in well applications to evaluatea variety of formation and well equipment related characteristics, suchas water breakthrough, leak detection, and gas lift monitoring andoptimization.

In the embodiment illustrated in FIG. 1, fiber optic system 20 isutilized in a well related application with the control unit 26positioned generally at a surface location and optical fiber sensor 22extending into a wellbore 28. Wellbore 28 may be formed in a geologicalformation 30 holding desired production fluids, such as hydrocarbonbased fluids that may be in the form of oil or gas. In manyapplications, wellbore 28 is lined with a wellbore casing 32 throughwhich perforations 34 are formed to enable the flow of fluids betweengeological formation 30 and wellbore 28. In this application, wellbore28 extends downwardly from a wellhead 36 positioned at a surface 38,e.g. the surface of the earth or a seabed floor.

Optical fiber sensor 22 may be routed along wellbore equipment 40, e.g.a tubing string, deployed in wellbore 28. The wellbore equipment 40 maycomprise a variety of wellbore completions, servicing tools or otherequipment depending on the well related operation to be performed.Furthermore, the optical fiber sensor 22 can be routed within wellboreequipment 40, along the exterior of wellbore equipment 40, along theinterior or exterior of wellbore casing 32, or along a combination ofregions. The optical fiber sensor 22 is designed to sense the desiredparameter, e.g. temperature, along wellbore 28 or along a specificsection of wellbore 28.

The optical fiber sensor 22 comprises a plurality of optical fibers 42,as illustrated in FIG. 2. The optical fibers 42, e.g. a pair of opticalfibers 42, have ends 44 which are connected by an optical fiber loop 46to provide optical continuity extending between optical fibers 42. Theoptical fiber loop 46 is functionally connected to ends 44 by fusionwelding or other suitable connection processes that enable theestablishment of optical continuity. In the example illustrated, opticalfiber loop 46 is a high strength fiber segment that is packaged in aprotective housing 48. The fiber loop 46 is packaged in a manner thatprotects it during shipment and also from downhole environmentalconditions once installed. The protective housing 48, optical fiber loop46 and related packaging comprise a fiber loop optical turnaround 50. Inthis embodiment, the fiber loop optical turnaround 50 further comprisesan adjustment device 52 provided to allow selective adjustment ofoptical fiber loop size. By way of example, adjustment device 52 maycomprise a sleeve 54, e.g. a tube, slidably mounted over optical fibers42. By sliding sleeve 54 toward or away from optical fiber loop 46, thediameter of the loop can be adjusted to facilitate, for example,movement into protective housing 48 and subsequent expansion to thegreatest diameter possible as limited by the inside diameter ofprotective housing 48.

Proper selection of a suitable optical fiber with which to form opticalfiber loop 46 can be accomplished by a variety of methods. For example,lengths of optical fiber may be acquired for use in the opticalturnaround 50 through a combination of testing and statistical flawdistribution. The optical fiber can be selected so as to have astatistical probability of sufficiently high strength to reliably formthe optical fiber loop. In one example, lengths of optical fiber aretaken from a batch of select fiber and subdivided into three sections orlengths. One length of fiber is set aside for use as optical fiber loop46, while the other lengths of optical fiber are tested to determinetensile strength/break load. If the strength of the tested lengths offiber is sufficient to avoid experiencing damaging stress levels whencreating a loop size needed for the optical turnaround, the set asideoptical fiber is presumed suitable for use in forming loop 46. Only astatistically insignificant probability exists that the set aside fiberhas differing characteristics compared to those of the tested opticalfibers. An alternative approach is to select the optical fiber forforming loop 46 from a fiber spool that is batch tested. A single testis performed on a sample of the fiber to verify strength. Additionally,through the use of appropriate optical fiber during manufacture of anoptical fiber cable, it is feasible to create optical fiber loop 46 byexposing a sufficient length of optical fiber from the cable so that oneof the fibers can be looped and fusion spliced to a second fiber in thecable. It should be noted that in some embodiments optical fiber loop 46and optical fibers 42 can be formed from one continuous fiber. Use ofthese analysis and selection methods enables the determination ofoptical fiber having high strength for use in the optical turnaround. Bylocating suitable high strength fiber through selective/random testingand/or statistical/historical data, the optical fiber can be bent in asmall diameter while still ensuring long-term reliability. Theturnarounds discussed herein also can be formed with relatively shortoptical fiber loops, e.g. one meter or less, which further reduces theprobability of defects in the optical fiber turnaround.

Referring to FIG. 3, one embodiment of fiber loop optical turnaround 50is illustrated as combined with an optical fiber cable 56 to formoptical fiber sensor 22. In this embodiment, optical fiber loop 46 isestablished at the end of optical fiber cable 56 and isolated fromdirect contact with the well environment by housing 48. Housing 48 alsoprotects optical fiber loop 46 and optical fibers 42 from vibration andshock that may be incurred during installation of optical fiber sensor22 and during service within wellbore 28. Additionally, a pottingcompound 58 can be introduced into the interior of housing 48 to furtherprotect the optical fibers and optical fiber loop. In one embodiment,housing 48 is partially filled with potting compound to secure opticalfiber loop 46 within housing 48 after proper installation of the opticalfiber loop.

The housing 48 is sealed to optical fiber cable 56 to ensure fiber loop46 and fibers 42 are isolated from direct contact with the surroundingwell environment. In the embodiment illustrated, housing 48 and opticalfiber cable 56 are sealed together by a suitable cable seal assembly 60,such as an in-line splice. However, other methods of cable sealing canbe used. One example of a suitable seal assembly, illustrated in FIG. 3,is an Intellitite Dry-Mate Connector (EDMC-R) available fromSchlumberger Corporation.

Construction of fiber loop optical turnaround 50 can be carried outaccording to several methodologies. One suitable approach involvesinitially preparing optical fiber cable 56 by stripping back theencapsulation material, straightening the cable, and holding the opticalfiber cable via an appropriate assembly fixture or other mechanism. Thecable seal assembly 60 is then slid onto optical fiber cable 56, asillustrated in FIG. 3. Typically, the optical fiber cable 56 has a metaljacket which is removed for a length, and any filler material isstripped away to expose optical fibers 42. Sleeve 54, which may be inthe form of a polyimide tube, is then slid over optical fibers 42 andinserted into optical fiber cable 56 until only a small length of thetube remains exposed. The optical fiber loop 46 is then functionallycoupled to the ends 44 of optical fibers 42 by, for example, a fusionsplice. Housing 48 can then be at least partially filled with pottingcompound 58 to secure the fiber loop 46. Subsequently, sleeve 54 is slidtoward optical fiber loop 46 until the loop is small enough to beinserted into housing 48, and housing 48 is moved over the optical fiberloop 46 until the loop clears any restrictions. Sleeve 54 is then slid ashort distance back into optical fiber cable 56 to allow fiber loop 46to expand to, for example, the full inside diameter of housing 48. Aconnection end 62 of housing 48 is moved over optical fiber cable 56 andinto engagement with cable seal assembly 60 so that a seal can be formedbetween housing 48 and optical fiber cable 56.

Formation of the optical fiber turnaround in this manner avoids theaddition of a variety of components into the overall tubing string. Forexample, no mandrels or shrouds are required to mount and protect theoptical turnaround. Protection of optical turnaround 50 is achievedthrough the systems and procedures described above, resulting insignificant cost savings.

An alternate embodiment of optical turnaround 50 is illustrated in FIGS.4-6. In this embodiment, a single tube 64 is used for routing opticalfibers 42 and optical fiber loop 46. It should be noted that opticalfibers 42 and fiber loop 46 can all be part of a single optical fiberrouted through the optical turnaround 50.

As illustrated in FIG. 4, the tube 64 is deformed to create an opticalfiber turnaround region 66 having a span 68 greater than the undeformedinternal diameter 70 of tube 64. The deformation of tube 64 to createturnaround region 66 also enables the use of an optical fiber loop 46having a diameter greater than the internal diameter 70 of tube 64. Inthe embodiment illustrated, tube 64 comprises a deformable, metal tube.The tube 64 is pinched or otherwise deformed from its exterior to createspan 68 in one direction and a narrower structure in the perpendiculardirection, as further illustrated in FIGS. 5 and 6.

The optical fiber turnaround 50 illustrated in FIGS. 4-6 also can becombined with an insert 72 that is inserted into tube 64 so that itresides in optical fiber turnaround region 66. The insert 72 is sized toreceive optical fiber and to hold optical fiber loop 46. The insert 72also is sized to support tube 64 in optical fiber turnaround region 66(see FIG. 6) to prevent the tube from further collapsing under externalpressure.

In creating this embodiment of optical fiber turnaround 50, insert 72 isinitially placed within tube 64 at the desired optical fiber turnaroundregion 66. An appropriate pressing tool is then used to pinch tube 64from the outside to reduce its dimension in the direction of pinchingand to increase its dimension in the opposite or perpendiculardirection. The wall of tube 64 is pinched until it touches insert 72which allows the insert 72 to support tube 64 against further collapse.The extremities of tube 64 on one or both sides of optical fiberturnaround region 66 can remain undeformed to enable connection to othertubes or to enable termination using suitable pipe termination fittings.

As further illustrated in FIGS. 7 and 8, insert 72 may comprise apassage 74 through which optical fiber loop 46 extends. The passage 74may have a curved portion 76 or other suitably shaped portion to enablethe optical fiber loop to be placed inside tube 64 in a desired shapeand curvature. Furthermore, curved portion 76 may be formed with atrough 78, when viewed in cross-section, to hold and protect the opticalfiber loop 46. By way of example, insert 72 also may comprise agenerally flat midsection 80 positioned between a pair of a larger ends82, as illustrated best in FIG. 8.

The optical fiber loop 46 can be formed by allowing a single opticalfiber 42 to be routed through passage 74 and around at least a portionof insert 72 until it is allowed to turn around and extend back upthrough tube 64. The diameter of the optical fiber loop is larger thanthe inside diameter 70 of tube 64 and may, for example, be in the rangeof more than 1 and less than 1.57 times the inside diameter 70. In manyapplications, a suitable diameter for optical fiber loop 46 is in therange of 1.1 to 1.4 times larger than the inside diameter 70 of tube 64.

In some embodiments, optical fiber loop 46 and the optical fibersections 42 extending from loop 46 can be further protected by anauxiliary sheath or tube 80 disposed around the optical fiber. Theauxiliary tube 80 can be made from appropriate, flexible materialsincluding polytetrafluoroethylene (PTFE) or thin-walled metal.

Another embodiment of insert 72 is illustrated in FIGS. 9 and 10. Thislatter embodiment is similar to the embodiment described with respect toFIGS. 7 and 8, but it includes a lengthened section 84, as bestillustrated in FIG. 9. A distal end 86 of section 84 is collapsed onitself (see FIG. 10) to enable the end of the insert and/or the end oftube 64 to be closed. Distal end 86 can be sealed by a linear weld 88 orother suitable sealing mechanism.

The embodiments of optical turnaround 50 can be formed from a variety ofmaterials and components. Additionally, the optical turnarounds 50 canbe used to facilitate construction of a variety of optical fiber sensorsystems that are used in many environments and applications. The opticalfiber sensor system and turnaround are suited to well relatedapplications, but the system and methodology also can be applied inother applications.

Accordingly, although only a few embodiments of the present inventionhave been described in detail above, those of ordinary skill in the artwill readily appreciate that many modifications are possible withoutmaterially departing from the teachings of this invention. Suchmodifications are intended to be included within the scope of thisinvention as defined in the claims.

1. A method of utilizing an optical fiber, comprising: exposing opticalfibers at an end of an optical fiber cable; connecting ends of theoptical fibers in an optical fiber loop; and inserting the optical fiberloop into an optical turnaround housing.
 2. The method as recited inclaim 1, further comprising: deploying a slidable tubing over theoptical fibers at the end of the optical fiber cable; sizing the opticalfiber loop for insertion into the optical turnaround housing by slidingthe tubing toward the optical fiber loop; and following insertion intothe optical turnaround housing, moving the tubing to allow expansion ofthe optical fiber loop.
 3. The method as recited in claim 2, whereindeploying comprises deploying a polyimide tubing over the opticalfibers.
 4. The method as recited in claim 1, wherein exposing comprisesexposing a pair of optical fibers.
 5. The method as recited in claim 4,wherein connecting comprises fusion splicing the optical fiber loop tothe pair of optical fibers.
 6. The method as recited in claim 2, whereinmoving the tubing comprises moving the tubing until the optical fiberloop fully spans an inside diameter of the optical turnaround housing.7. The method as recited in claim 2, further comprising placing apotting compound in the optical turnaround housing to secure the opticalfiber loop in the optical turnaround housing.